Speaking to former Foreign Secretary Sir Malcolm Rifkind, Clarke didn't hold back on his views on those hoping to take over from David Cameron.

The former Chancellor, who failed three times to be elected Tory Party leader, seemingly didn't realise the cameras were rolling and the mic was on as he made his comments.

Here are some of his views:

Michael Gove

"I think with Michael as Prime Minister we would go to war with at least three countries at once."

"He did us all a favour by getting rid of Boris. Having Boris as Prime Minister is ridiculous."

Andrea Leadsom

"I don’t think either Andrea Leadsom or Boris Johnson are actually in favour of leaving the European Union.

"She’s not of the tiny band of lunatics who think we can have a glorious economic future outside of the Single Market. So long as she understands she's not to deliver on some of the extremely stupid things she's been saying."

Theresa May

"Theresa is a bloody difficult woman, but you and I worked for Margaret Thatcher."

"She is good but she is too narrow on her department. She's been in the Home Office far too long."

Stephen Crabb

"I might give Stephen Crabb an encouraging vote first, but I don’t know what Crabb’s views are on most things."

Liam Fox

"He is much more right-wing than me."

Sir Malcolm later told LBC he was "not in the slightest bit upset" by the leaking of the clip.

He told Iain Dale: "It all adds to the sum of human happiness!"

Sir Malcolm added: "I can think of worse things that could have happened...I'm not in the slightest bit upset.

"What Ken and I were chatting about, for the most part, we'd have said perfectly happily in front of the microphones in any event."

Voting in the Tory leadership contest began today, and the contender with the lowest number of votes from MPs will be eliminated this evening.